The internal combustion engine generally predominates as a prime mover in auto-vehicles, motorboats and portable electrical power plants.
Strenuous efforts are being made to reduce the emissions and to increase engine efficiencies.
The value of higher efficiencies increases with the growing scarcity of engine fuel, coupled with higher fuel costs. Another reason for endeavouring to achieve improved efficiencies is because of the increasing greenhouse effect, which can be alleviated to some extent with improved engine efficiencies. Moreover, biological fuels capable of replacing fossil fuels will always be a scarce resource.
The Otto engine has low exhaust emissions as a result of successful catalyst technology although it also has a low efficiency, particularly at partial loads. The reason for this low efficiency is because of the necessity to restrict the compression ratio due to the need of preventing self-ignition (knocking). Throttling losses occur at partial loads, these losses normally being accompanied by high percentages of frictional losses, due to the fact that the engine is normally relatively large in relation to the average power taken from the engine.
Although the diesel engine has a satisfactory efficiency it also has the problem of particle and NOx-emissions.
Although it is possible to reduce these emissions, the costs involved and the ensuing problems concerning the reliability of the engine in operation cause the diesel engine to be viewed less attractively.
As a result, research scientists have become very interested in the use of homogenous compression ignition combustion (HCCI) as a method of dealing with NOx and particle-free combustion, CO and HC emissions with the aid of a simple oxidizing catalyst. The compression ratio will then suitably be such as to cause the point of ignition to lie in the proximity of that obtained in the compression ratio used in the case of diesel engines, resulting in highly efficient internal combustion engines. Combustion will also be rapid, regardless of speed-dependent turbulence. Although this rapid combustion is favourable with respect to efficiency, it is problematic with respect to noise and with respect to the permitted maximum fuel consumption per combustion cycle. Consequently, an HCCI-engine will normally have a lower maximum power output than a conventional engine.
The HCCI-combustion process can be controlled with a variable compression ratio or variable valve times. Both methods incur considerably more expense if the measures undertaken shall be added to an existing engine concept.
Vibrations are another problem incurred by piston engines. There are, in principle, two different causes for these disturbing vibrations, the best known being. the result of the acceleration of the pistons and the accompanying part of the crankshaft. The method of eliminating this vibration, which has a force amplitude that is quadratic with respect to engine speed, is to include many cylinders or balance shafts in the case of engines that have fewer than six cylinders. A four-cylinder engine with double the number of counter-rotating balance shafts is, in principle, fully balanced with respect to this vibration.
The other type of vibration is amplitude-independent of the speed. This is due to the necessity of slowing down the flywheel crankshaft in order to obtain the compression work that imparts a torque amplitude to the engine body. Subsequent to combustion, the crankshaft will be accelerated under the influence of the useful work obtained from the expansion of the combustion gas with a further torque impulse on the engine body as a result. The above problem can also be lessened in this case by including many cylinders. Distinct from the vibrations caused by piston acceleration, it is not possible to eliminate these vibrations irrespective of the number of cylinders that are provided on a common crankshaft. These torque vibrations impair engine operation at high torques on very low engine speeds. This drop in engine performance is, however, the most energy effective at low power outputs.
Patent specification WO88/05862 teaches an internal combustion engine that includes counter-acting cylinders whose crankshafts are synchronized with the aid of a fixed gear wheel system that includes two gear wheels and two intermediate gear wheels on fixed bearing axles. One crank-shaft mounted gear wheel of the gear wheel system is arranged to allow its angle relative to its crankshaft to be changed so as to alter its phase position, through the medium of a separate operating device which is arranged as a harmonic gear or as a variable splined coupling, or as an additional operating device for changing the relative angular position of two shafts between two conical gears.